/*
 * Copyright 2020 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package com.aduib.boot.common.buffer;

/**
 * Internal primitive map implementation that is specifically optimised for the runs availability
 * map use case in {@link BufferChunk}.
 */
final class LongLongHashMap {
  private static final int MASK_TEMPLATE = ~1;
  private final long emptyVal;
  private int mask;
  private long[] array;
  private int maxProbe;
  private long zeroVal;

  LongLongHashMap(long emptyVal) {
    this.emptyVal = emptyVal;
    zeroVal = emptyVal;
    int initialSize = 32;
    array = new long[initialSize];
    mask = initialSize - 1;
    computeMaskAndProbe();
  }

  public long put(long key, long value) {
    if (key == 0) {
      long prev = zeroVal;
      zeroVal = value;
      return prev;
    }

    for (; ; ) {
      int index = index(key);
      for (int i = 0; i < maxProbe; i++) {
        long existing = array[index];
        if (existing == key || existing == 0) {
          long prev = existing == 0 ? emptyVal : array[index + 1];
          array[index] = key;
          array[index + 1] = value;
          for (; i < maxProbe; i++) { // Nerf any existing misplaced entries.
            index = index + 2 & mask;
            if (array[index] == key) {
              array[index] = 0;
              prev = array[index + 1];
              break;
            }
          }
          return prev;
        }
        index = index + 2 & mask;
      }
      expand(); // Grow array and re-hash.
    }
  }

  public void remove(long key) {
    if (key == 0) {
      zeroVal = emptyVal;
      return;
    }
    int index = index(key);
    for (int i = 0; i < maxProbe; i++) {
      long existing = array[index];
      if (existing == key) {
        array[index] = 0;
        break;
      }
      index = index + 2 & mask;
    }
  }

  public long get(long key) {
    if (key == 0) {
      return zeroVal;
    }
    int index = index(key);
    for (int i = 0; i < maxProbe; i++) {
      long existing = array[index];
      if (existing == key) {
        return array[index + 1];
      }
      index = index + 2 & mask;
    }
    return emptyVal;
  }

  private int index(long key) {
    // Hash with murmur64, and mask.
    key ^= key >>> 33;
    key *= 0xff51afd7ed558ccdL;
    key ^= key >>> 33;
    key *= 0xc4ceb9fe1a85ec53L;
    key ^= key >>> 33;
    return (int) key & mask;
  }

  private void expand() {
    long[] prev = array;
    array = new long[prev.length * 2];
    computeMaskAndProbe();
    for (int i = 0; i < prev.length; i += 2) {
      long key = prev[i];
      if (key != 0) {
        long val = prev[i + 1];
        put(key, val);
      }
    }
  }

  private void computeMaskAndProbe() {
    int length = array.length;
    mask = length - 1 & MASK_TEMPLATE;
    maxProbe = (int) Math.log(length);
  }
}
